Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 329 AM EDT Wed Sep 18 2024 Valid 12Z Wed Sep 18 2024 - 12Z Fri Sep 20 2024 ...Very heavy rainfall and flash flooding possible in Montana today... ...Severe thunderstorms possible in the northern and central Plains and Upper Midwest today and Thursday... A strong occluded low will bring hazardous weather to Montana today as it lingers over the state. Strong upslope flow along the northern Rockies on the backside of the low will result in showers and thunderstorms with very heavy rainfall totals. A Slight Risk of Excessive Rainfall (level 2/4) is in effect for portions of Montana where scattered flash flooding will be possible. Wintry precipitation will also be possible in the high elevations of the northern Rockies. In addition to precipitation hazards, a strong pressure gradient in the vicinity of the central low will result in strong, gusty winds across the region. High Wind Watches and Warnings are in effect for portions of Montana and Wyoming where winds are forecast to be 30-40 mph with gusts up 60 mph. The low will gradually lift north into southern Canada Thursday and Friday, and rain and winds will begin to relax. The strong low pressure system will also push a cold front across the Plains and Upper Midwest through Friday. A line of showers and thunderstorms will move east ahead of the cold front, and the environment will support the development of scattered severe thunderstorms. The Storm Prediction Center has highlighted portions of the Plains and Upper Midwest with a Slight Risk of Severe Thunderstorms (level 2/5) today and again on Thursday. Potential severe storm hazards will include damaging wind gusts, large hail, and a few tornadoes. Shower and thunderstorm coverage will expand into the Great Lakes and Mid-Mississippi and Ohio Valleys on Friday as the cold front continues to trek east. Elsewhere, two coastal lows will sandwich the continental United States, one moving south along the West Coast and one moving north along the East Coast. The West Coast low will bring precipitation to the Northwest this morning, then to the Great Basin and California later today into Thursday. Precipitation will fall mainly in the form of showers and thunderstorms, but some wintry precipitation will be possible in the Sierra Nevada. The low will weaken on Friday, and precipitation will taper off. The East Coast low will gradually deepen offshore of the Mid-Atlantic over the next few days with a slow-moving frontal boundary extending southwest from the low. Showers and storms will be possible for the Mid-Atlantic, coastal Northeast, Southeast, and Florida. This system will also produce gusty winds over the coastal waters, which has prompted Small Craft and Coastal Flood Advisories along the Mid-Atlantic Coast. Temperature-wise, the West will experience well below average temperatures in the wake of the strong frontal system in the Plains, while the Central U.S. experiences well above average temperatures with southerly flow ahead of the Plains system. Highs over the next few days will only be in the 60s and 70s for much of the West, while highs in the Plains and Midwest reach the 80s and 90s. A few near-record high temperatures will be possible in the southern Plains where highs will approach 100 degrees. Above average temperatures will also be observed in the Northeast under an upper level ridge, and near to slightly below normal temperatures will be observed in the Mid-Atlantic and Southeast. Dolan Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php